Flowable materials contained in packages are sometimes subject to settling, or otherwise require mixing before they can be dispensed or otherwise exhibit the characteristics expected of them. Low viscosity materials (e.g. water), can usually be sufficiently mixed simply by shaking the package vigorously before opening it. However, for viscous materials (e.g. pastes, slurries, etc.), that method is often not effective, so direct stirring of the material is required, typically by inserting a mixing element into the package through its opening. Unfortunately, because viscous materials are often very sticky, a significant amount of that material will likely stick to whatever mixing element is inserted into the package as it is being withdrawn, making it very cumbersome and time consuming to mix the material. What is clearly needed is a closure that both covers the package opening and accommodates the insertion and withdrawal of a desired mixing element, such that when the said mixing element is withdrawn, the closure strips off substantially whatever material residue is sticking to the mixing element, thus preventing it from escaping the vessel.